The Wilcoxon signed rank test is used when a researcher wants to analyze two related (as opposed to independent) samples. Related samples are connected in some way. For example, a researcher will try to equalize groups on IQ, gender, age, or some other variable. The groups are matched on these variables. Another example of a related sample is when the same group is both pretested and posttested. Each individual is tested on two different occasions (as with the t test for correlated means).
This test is very easy to use. The researcher simply lines up the pairs of related subjects and then determines how many times the paired subjects in one group scored higher than those in the other group. If the groups do not differ significantly, the totals for the two groups should be about equal. If there is a marked difference in scoring (such as many more in one group scoring higher), the difference may be statistically significant. The probability of this occurrence can be determined by consulting the appropriate statistical table.
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